1. Field of the Invention
The present invention relates to magnetic printers and in particular to magnetic printers for generating machine and man-readable printed bar patterns on labels and other permanent recording mediums for use as a computer input, such as in grocery product coding.
2. Description of the Prior Art
The concept of magnetic printing, sometimes called ferromagnetography has existed for over 25 years but has been fraught with problems including generating a magnetized image on a magnetizable recording material, selectively placing a visible material on the magnetized portions of the recording media ("toning"), and transferring this visible material image to a permanent medium such as paper. Prior art devices have overcome or substantially reduced several of these problems and provided printers of reasonable quality. However, most of these printers have been expensive and have not been able to produce highly accurate printing. Such printing is imperative in the field of bar pattern coding for automatic grocery checkout systems.
Some of these problems, such as the writing of information onto a recording tape, have been successfully dealt with; such as disclosed in U.S. Pat. No. 3,735,416, entitled "Magnetic Printing System", U.S. Pat. No. 3,254,626 entitled "High Speed Letter Printing System" and U.S. Pat. No. 2,986,608 entitled "Magnetic Recording Cross-Talk Elimination" wherein the proper generation of a small magnetized area on a recording tape has been achieved with the elimination of unwanted magnetizing of adjacent areas. However, the generation of bars of varying width and uniform blackness has not been successfully achieved.
Also, the fixing of toner material on a recording medium, such as a paper sheet, has been substantially solved. The solution is the use of a toner comprising a powder containing small particles of magnetizable material surrounded by a heat fusible resin, wherein the resin is fused to the recording medium by a heater, such as a radiant heater. However, the printing of labels on a backing strip has remained a problem with such fusing or fixing devices since the backing strip must also be heated. Close placement of labels is also not possible unless the backing strip reverses direction after placement within the heater. The present invention overcomes this problem by peeling the label from the backing strip prior to the fusing operation.
Another problem is the application of the toner to the magnetized area of the recording tape. Typically, because the toner is a powder consisting of a magnetized material imbedded within a heat fusible resin, the application of this toner to the recording tape has presented difficulty in obtaining a clear, sharp image consisting of toner fully applied to magnetized regions of the tape and not applied to unmagnetized regions. In U.S. Pat. No. 3,735,416, entitled "Magnetic Printing Systems," a toner applicator/cleaner is disclosed using rotating bristles for transferring toner particles from a reservoir to an aperture over which the recording tape passes. However, the use of rotating bristles has the problem of not always applying a uniform and adequate amount of toner to the recording tape.
In U.S. Pat. No. 3,859,959, entitled "Magnetic Toner Applicator," a toner ring of magnetic material transports toner material to an aperture having an inclined edge where the toner impinges or the edge or "dam" and builds so as to more evenly apply the toner to a passing recording tape. However, if the magnetized recording tape comes too close to the magnetic toner ring, the magnetic field of the ring may deform the magnetic pattern on the tape; thus degrading or ruining the data to be printed. Also in U.S. Pat. No. 3,392,432, entitled "Magnetic Roller for Electrophotographic Development," a magnetic roller is disclosed for applying toner powder to a latent electrostatic image by using magnetizable carrier particles. Because the roller is used with electrostatic latent images, the close proximity of the roller to the latent image will not distort the image. Such close proximity could seriously deteriorate the magnetic latent image of the recording tape in a magnetic printer. Furthermore, the disclosed switchable magnetic field on the periphery of the roller in the '432 patent would have no apparent beneficial practical effect for magnetic printing since magnetic printers typically use a differnt type of toner mixture.
The basic problem in toning is to closely expose the magnetic latent image to a large number of toner particles having random magnetic orientations so that some will have the proper orientation and magnetically adhere to the latent image. Thus, the uniform, clean, sharp deposition of toner to the magnetized portion of the recording tape has remained a problem even when printing text. More importantly a sharp, clear deposition of toner is imperative in bar pattern coding used in the grocery industry for automatic checkout. Here, a bar pattern of light and dark bars is used as a computer input for generating twelve digits that identify the product to be sold. The bar pattern is scanned with a light wand or a laser scanner. The reflected light from a spot ranging from 0.005 to 0.008 inch in diameter as the wand or scanner crosses the pattern generates, by a photosensitive device, a voltage proportional to the light and dark bars. Any void in the dark bars or spots in the light bars could alter the reflected light to the extent that a false digit is read by the computer.
The present invention overcomes these problems in the prior art by providing a toner applicator incorporating a revolving longitudinally disposed toner drum having an outer permanently magnetized periphery consisting of magnetic poles arranged in a helical or other pattern about the periphery of the drum. This polar magnetic surface attracts toner particles form a toner reservoir, forming a toner layer. The rotating drum thus transports the toner around its entire outer periphery. The recording tape approaches and is spaced from the uppermost region of the rotating drum. Between the tape and the toner drum there is a plurality of magnetizable wires that magnetically and mechanically interact with the toner layer to form sweeping ridges of toner about each of the wires. These ridges form a fluidized magnetic toner bed between the wires and the tape for efficient transferral of the toner to the magnetized region of the recording tape. The toner particles within this fluidized bed of ridges are in vigorous random motion and many of them are easily attracted to the magnetized regions of the recording tape so as to form a pattern of toner corresponding to the previously recorded magnetic image written on the recording tape by the recording heads.
Electrically charged wires have been used in electrostatic printers. These wires are used for electrostatically charging a sheet of paper to assist the transfer of a toner image from a photoconductor element to the paper. The wires do not form magnetic fields for forming ridges of magnetic toner, but only electrostatically charge a piece of paper so that the paper can electrostatically capture a toner image on a photoconductor element. The magnetizable wires of the present invention do not have any electrical potential impressed on them and they are not used to electrostatically charge a sheet of paper. Thus, although prior art devices, such as U.S. Pat. No. 3,620,617, entitled "Electrophotographic Apparatus with Improved Toner Transfer," use wires to promote toner transfer, these prior art devices are concerned with an entirely different type of toner transfer and in no way suggest or disclose the use of magnetizable wires in applying toner to magnetized regions of a magnetic recording tape or other magnetic recording medium.
Excess toner particles that inadvertently, mechanically adhere to the recording tape in regions that are not magnetized, that adhere to toner particles adhering to magnetized regions, are easily removed by use of an air knife of this invention blowing a sheet of air at an acute angle at the recording tape. The transfer of the recorded toner image on the recording tape to a label is accomplished by properly synchronizing the actuation of pinch rollers so as to transfer the image to pressure sensitive labels at the correct time. This insures proper registration of the image onto the label. The label or other pressure sensitive paper is synchronously removed from its paper backing and transferred to a conveyor passing through a heater to fuse the toner to the label. The label may then be re-applied to the backing strip for use in applying the label to packages.